Gas turbine fuel flow metering control system

ABSTRACT

A &#39;&#39;&#39;&#39;free-wheeling&#39;&#39;&#39;&#39; flow divider actuated by pressure of the liquid fuel meters fuel to the separate combustion chambers of a gas turbine. The actual fuel flow rate is sensed by measuring the speed of a shaft turning several positive-displacement flow dividing elements and is compared to a desired total fuel flow command signal. The difference or error signal operates a servo mechanism to adjust fuel flow rate to the &#39;&#39;&#39;&#39;free-wheeling&#39;&#39;&#39;&#39; flow divider.

nited States Patent [1 1 I osa [ GAS TURBINE FUEL FLOW METERING CONTROLSYSTEM [75] Inventor: Hugh E. Rosa, Schenectady, NY.

[73] Assignee: General'Electric Company,

Schenectady, NY.

[22] Filed: July 16, 1971 [21] App]. No.: 163,353

[52] U.S.'Cl'. 60/39.28 R, 137/115, 137/608,

[5 1] Int. Cl F02c 9/08, F02c 9/10 [58] Field of-Search 60/3928 R, 39.28T;

[56] References Cited UNITED STATES PATENTS 2,936,028 5/1960 Gatzemeyer60/3928 R FREQUENCY TO VOLTAGE SIGNAL June12, 1973 3,316,712 5/1967Tyler 60/3928 R 2,842,108 7/1958 Sanders 123/102 3,212,261 10/1965 Rose60/3928 R 3,274,768 9/1966 Klein 60/3928 R Primary Examiner-Clarence R.Gordon Attorney william C. Crutcher, James W. Mitchell, Frank L.Newhauser et a1.

[57] ABSTRACT A free-wheeling flow divider actuated by pressure of theliquid fuel meters fuel to the separate combustion chambers of a gasturbine. The actual fuel flow rate is sensed by measuring the speed of ashaft turning several positive-displacement flow dividing elements andis compared to a desired total fuel flow command signal. The differenceor error signal operates a servo mechanism to adjust fuel flow rate tothe freewheeling flow divider.

8 Claims, 3 Drawing Figures GAS TURBINE FUEL CONTROL GAS TURBINE FUELFLOW METERING CONTROL SYSTEM BACKGROUND OF THE INVENTION This inventionrelates generally to fuel systems for gas turbines having combustionchambers supplied separately with liquid fuel. More particularly, itrelates to metering of fuel to one or more combustion chambers at adesired rate of flow in accordance with a desired overall fuel flowcommand signal.

A modern gas turbine power plant has several combustion chambers intowhich fuel is injected through nozzles and burned. In order to obtainuniform temperature distribution around the gas turbine circumference,equal flow rates of fuel should flow to the individual combustionchambers. Many operating difficulties will ensue if there are localareas of excessively high temperature. Many types of metering deviceshave been suggested in the prior art for dividing a total flow of fuelinto equal portions and delivering it at a desired rate of flow into thecombustion chambers.

A device which has been commonly used to deliver fuel at a controlledrate as well as divide it into equal portions is a synchronized set ofpositive displacement gear pumps, such as disclosed in US. Pat. No.2,936,028 issued to J. B. Gatzmeyer, et al. on May 10, 1960 and assignedto the present assignee. In the Gatzmeyer et al. patent, a hydraulicdriving motor is used to rotate the set of gear pumps at a speeddetermined by a variable displacement hydraulic pump driving thehydraulic motor. As the speed of the hydraulic motor is adjusted inaccordance with a fuel flow demand sigtrail, a fuel flow bypass valve issimultaneously actuated to return fuel to the inlet of the main fuelpump. Although the foregoing system has been very successful indelivering fuel to the combustion chambers at metered flow rates,calibration is required between positioning of the bypass valve andspeed setting of the hydraulic motor. This calibration is affected bythe mechanical condition of the pump components.

Other systems have been proposed for gas turbine flow dividers. U.S.Pat. No. 2,599,680 to Weeks shows a flow divider which is driven at avarying speed in response to a pressure differential across one of theflow metering elements. The inlet flow rate to the group of meteringdevices is controlled by a bypass valve similar to the Gatzmeyer patent,but there is no direct correlation between the speed at which themetering devices are driven and the rate at which fuel is supplied tothe metering devices.

British Pat. No. 819,760 and U.S. Pat. No. 2,566,373 to E. M. Reddingshow gas turbines using freewheeling flow dividers which do not requirea driving device as in the foregoing Gatzmeyer and Weeks patents, butare rather driven by the pressure of the fuel supplied to the meteringelements. Calibration between the total fuel flow control device and therate of fuel actually supplied by the metering elements is dependentupon the mechanical condition of the pump as in the foregoing patents.

Systems have also been proposed which purport to control fuel flow inresponse to flow rate or fuel pressure, such as US 'Pat. No. 2,851,855to Gamble, No.

3,128,603 to Haigh and No. 3,413,806 to Belke et al.

However these systems do not serve to divide the fuel flow whilecontrolling the flow rate.

Accordingly, one object of the present invention is to provide animproved flow dividing control system for a gas turbine for preciselymetering fuel flow from the individual elements in response to a desiredfuel flow command signal supplied to the system.

Another object of the invention is to provide an improved control systemfor a freewheeling flow divider actuated by pressure of the fuel, butsupplying fuel at a controlled rate of flow to the combustion chambers.

Another object of the invention is to provide an improved flow dividingcontrol system which may be used with several different types of fuelsupply devices.

DRAWINGS The invention, both as to organization and method of practice,together with further objects and advantages thereof, will best beunderstood by reference to the following specifications, taken inconnection with the accompanying drawings, in which:

FIG. 1 is a simplified schematic drawing of a gas turbine with a fuelflow dividing control system using a positive displacement fuel pump,and

FIG. 2 is a modified form of the invention using a variable displacementfuel pump, and

FIG. 3 is another modification using a throttling valve to control flowfrom a pressurized fuel main.

SUMMARY OF THE INVENTION Briefly stated, the invention is practiced byproviding means to .control fuel inlet flow rate to a flow dividercomprising a synchronized set of positive displacement meteringelements. Speed of the set (and hence flow rate) is measured andcompared to a fuel fiow command signal. The resulting error signaloperates a servo mechanism which adjusts actual flow rate to cause it tocorrespond to desired flow rate.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 of thedrawing, a gas turbine 1 has a number of individual combustion chambers2 disposed about its periphery. The fuel nozzle in each combustionchamber is fed from a separate fuel line 3, supplied in parallel flowrelationship from a metering flow divider 4.

Flow divider 4 is constructed so as to operate a number of positivedisplacement metering devices such as individual gear pumps 5. The gearpumps 5 all are synchronized to turn at the same speed. For this purposethey may be mounted on a common shaft 6 as indicated or alternativelymay be arranged in a circular configuration and geared to a commonsynchronizing pinion.

The metering elements are constructed so as to be rotated by the liquidpressure difference between the inlet and outlet of the flow divider.One such suitable flow divider is manufactured by Roper Pump Company,Commerce, Ga., Model No. 2901.

The speed of shaft 6 and hence the speed of each of the gear pumps 5 isindicated by a two-toothed wheels 7 and two magnetic reluctance sensors8 producing pulses as the wheels 7 turn. One wheel 7 and one sensor 8would be sufficient to measure the speed, but two are employed toprovide an added measure of safety. Alternatively, a tachometergenerator may be substituted for toothed wheel 7, sensor 8, andconverter 27 to give a voltage proportional to speed.

Since liquid fuel is essentially incompressible and since the gear pumps5 are positive displacement devices, i.e., have practically no leakage,the speed of shaft 6 is proportional to the rate of fuel flow suppliedthrough each of the individual fuel lines 3 to the gas turbinecombustion chambers.

The fuel supply system for the flow divider 4 comprises a fuel supplytank 9, motor driven pump 10 and a positive displacement pump 11. Pump11 is driven at a constant rate of speed by a motor 12 (or alternativelyfrom the gas turbine shaft) so as to supply a constant rate of fuel flowthrough pipe 13. A line 14 carries a portion of the total flow to theinlet of flow divider 4, while the remaining portion of fuel flowsthrough bypass line 15, as controlled by valve 16, back to the inlet ofthe displacement pump 11. Thus the position of bypass valve 16 serves tovary the rate of fuel flow furnished to flow divider 4.

A servo valve 17 which may be of the type manufactured by Moog ControlDivision, East Aurora, N. Y., Model No. 77-131, positions bypass valve16 in response to the output of an operational amplifier 18. The generalcharacteristic of such a valve 16 is that it provides an output flowproportional to input current. Operational amplifier 18 is acommercially known device which can be connected as a summer so that theoutput voltage is the sum of the magnitude and polarity of the appliedinput voltages. Other types of known summing devices or comparators,with or without amplification of the output signal may be substituted.

The fuel flow command signal used to set the desired fuel flow rate tothe gas turbine is produced by a gas turbine fuel control systemindicated generally at 19. This may be one of several types and isresponsive to various operating parameters of the gas turbine such as acompressor speed signal 20, compressor pressure signal 21, flamedetector signal 22, exhaust temperature signal 23, and load turbinespeed signal 24. Various operator-controlled input signals are indicatedat 25. The fuel control 19 may be of the type shown in U.S. Pat. No.3,520,133 issued to A. Loft et al., on July 14, 1970, known by theassignees trade-mark SPEED- TRONIC, and assigned to the presentassignee, this patent being incorporated herein by reference. The outputsignal at 26 is a voltage representative of a desired fuel flow to thegas turbine. It is applied as one input to operational amplifier 18.

The other input to operational amplifier 18 is a signal representingactual rate of fuel flow obtained from the speed of the gearsynchronizing shaft in the freewheeling flow divider 4. Pulses fromsensors 8 are converted in a converter 27 to a voltage proportional toactual fuel flow, since the frequency of pulses is proportional to fuelflow as explained previously.

OPERATION A fuel flow command signal is applied as a voltage to outputline 26 from the gas turbine fuel control 19 in response to operatingconditions of the gas turbine. This voltage is applied at the input tooperational amplifier 18 with a voltage obtained from rotational speedofthe flow divider elements 5. The error signal actuates servo valve 17to reposition bypass valve 16 so as to adjust the total flow rate toflow divider 4 so as to reduce the error to 0. System is independent ofthe condition of the components ofthe main flow pump 11 or thecalibration of the bypass valve 16. Thus actual metered MODIFICATION 1FIG. 2 shows a modified form of the invention while omitting some of thedetails shown in FIG. 1 which are not necessary to an understanding ofthe invention. Identical reference numerals are used where theycorrespond to FIG. 1. Rather than employing a positive displacement fuelpump and a bypass line as in FIG. 1, a variable displacement pump 28 isused. This may be one of many known types such as Model No. 226Al249manufactured by New York Air Brake Co. having a variable stroke. Thepump stroke is set by a servo device 29, which is often an integral partof the pump in commercial devices of this type.

The operation of the FIG. 2 modification is the same as in FIG. 1. Theoutput from operational amplifier 18 representing a different or errorsignal between actual and desired fuel flow rate signals operates servo29 and readjusts the delivery from pump 28 so as to make actual flowcorrespond to desired flow. As before, the pressure at the outlet frompump 28 provides the impelling force to drive the synchronized set ofmetering devices in the flow divider 4.

MODIFICATION 2 FIG. 3 shows another modification, wherein fuel deliveredto the gas turbine is supplied from a high pressure fuel main 31. Anexample would be a branch line from the outlet of a liquid fuel pipeline pumping station serviced by the gas turbine.

Fuel under pressure suitable for driving the free wheeling flow divider4 is supplied through the line 31 and the flow rate is varied by meansof a throttling valve 32 actuated by a hydraulic piston 33. Piston 33 ispositioned by a hydraulic servo valve 34.

Operation of the FIG. 3 modification is much the same as previouslydescribed. Speed of the synchronizing shaft of the free-wheeling flowdivider 4 is converted to a fuel flow rate voltage signal at 27 andcompared in operational amplifier 18 with a flow command signal. Theerror signal corrects the position of the hydraulic piston 33 so as toincrease or reduce flow rate to the flow divider and reduce the error tozero.

Thus, there has been described an improved flow dividing fuel system fora gas turbine which is less complex than previous systems andfurthermore does not depend on precise positioning ofa series ofmechanical components to control output. Its operation is independent ofthe wear of various components such as the pumps supplying the liquidfuel and the calibration of the other various components.

While there has been shown what is considered to be the preferredembodiment of the invention and two modifications thereof, it is ofcourse understood that various other modifications may be made therein,and it is intended to cover in the appended claims all suchmodifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a gas turbine fuel flow dividing control system of the type havinga plurality of individual fuel lines to be furnished with equal meteredflow rates of fuel for the combustion chambers of a gas turbine inresponse to a fuel flow command signal, the improvement comprising:

a source of liquid fuel under pressure,

a free-wheeling flow divider including a plurality of positivedisplacement metering elements supplied from an inlet and connected at aplurality of outlets to said individual fuel lines, said elements beingconstructed to rotate when subjected to a pressure difference,

rotatable synchronizing means causing said elements to turn in unison,

flow rate control means supplying an adjustable flow rate of liquid fuelfrom said source to said inlet of the flow divider at a pressuresufficient to actuate said'metering elements,

means responsive to the speed of said synchronizing means for producinga signal proportional to actual flow rate, and

summing means arranged to compare said flow rate signal to said fuelflow command signal and having an output connected to actuate said flowrate control means.

2. The combination according to claim 1, wherein said flow rate controlmeans comprises a positive displacement pump with a bypass valveconnected at the pump outlet and arranged to return flow to the pumpinlet.

3. The combination according to claim 1, wherein said flow rate controlmeans comprises a variable displacement pump with means to control thepump displacement stroke.

4. The combination according to claim 1, wherein said flow rate controlmeans comprises a flow throttling valve connected between saidpressurized fuel source and said flow divider.

5. The combination according to claim 1, wherein said metering elementsare gear pumps and wherein said synchronizing means is a common shaftcarrying said gear pumps.

6. The combination according to claim 1, wherein said metering elementsare gear pumps and wherein said synchronizing means is a common piniongeared to said gear'pumps.

7. The combination according to claim 1, wherein said speed responsivemeans comprises a toothed wheel connected to be rotated by saidsynchronizing means, a variable magnetic reluctance sensor for providingpulses in response to rotation, and a converter for producing a voltageproportional to pulse frequency.

8. The combination according to claim 1, wherein said speed responsivemeans comprises a tachometer generator connected to be rotated by saidsynchronizing means.

1. In a gas turbine fuel flow dividing control system of the type havinga plurality of individual fuel lines to be furnished with equal meteredflow rates of fuel for the combustion chambers of a gas turbine inresponse to a fuel flow command signal, the improvement comprising: asource of liquid fuel under pressure, a free-wheeling flow dividerincluding a plurality of positive displacement metering elementssupplied from an inlet and connected at a plurality of outlets to saidindividual fuel lines, said elements being constructed to rotate whensubjected to a pressure difference, rotatable synchronizing meanscausing said elements to turn in unison, flow rate control meanssupplying an adjustable flow rate of liquid fuel from said source tosaid inlet of the flow divider at a pressure sufficient to actuate saidmetering elements, means responsive to the speed of said synchronizingmeans for producing a signal proportional to actual flow rate, andsumming means arranged to compare said flow rate signal to said fuelflow command signal and having an output connected to actuate said flowrate control means.
 2. The combination according to claim 1, whereinsaid flow rate control means comprises a positive displacement pump witha bypass valve connected at the pump outlet and arranged to return flowto the pump inlet.
 3. The combination according to claim 1, wherein saidflow rate control means comprises a variable displacement pump withmeans to control the pump displacement stroke.
 4. The combinationaccording to claim 1, wherein said flow rate control means comprises aflow throttling valve connected between said pressurized fuel source andsaid flOw divider.
 5. The combination according to claim 1, wherein saidmetering elements are gear pumps and wherein said synchronizing means isa common shaft carrying said gear pumps.
 6. The combination according toclaim 1, wherein said metering elements are gear pumps and wherein saidsynchronizing means is a common pinion geared to said gear pumps.
 7. Thecombination according to claim 1, wherein said speed responsive meanscomprises a toothed wheel connected to be rotated by said synchronizingmeans, a variable magnetic reluctance sensor for providing pulses inresponse to rotation, and a converter for producing a voltageproportional to pulse frequency.
 8. The combination according to claim1, wherein said speed responsive means comprises a tachometer generatorconnected to be rotated by said synchronizing means.